Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, not destructive. Description adds deterministic daily card (same for all listeners, midnight MST), random single/three, and output contents (meanings, astrology, suit). However, the card_name parameter behavior is not mentioned in the description (only in schema).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.